Abstract [en]

Cerebrovascular disease is the second leading cause of death worldwide and determining plaque vulnerability is critical to early intervention, selecting appropriate treatment, and reducing mortality rates. Shear wave elastography (SWE) is an ultrasound-based technique to characterize the mechanical properties of tissue and pulse wave imaging (PWI) is most commonly used to measure arterial stiffness by estimating the propagation speed of the pulse wave generated from left ventricular ejection. In this study, SWE and PWI were used to characterize three homogeneous plaque mimicking inclusions in three common carotid artery phantoms by using phase velocity (PV) and group velocity (GV) analysis as well as estimating the pulse wave velocity (PWV) using PWI. Thereafter, the estimated Young’s modulus values were compared in the phantom walls. The mean wave velocities in the plaques were 1.7 ± 0.2 m/s, 1.6 ± 0.1 m/s, and 2.5 ± 0.5 m/s calculated by PV, GV, and PWI, respectively. This was lower than the mean wave speeds measured in the vessel wall (3.8 ± 0.2 m/s, 3.5 ± 0.2 m/s, and 3.3 ± 0.1 m/s by PV, GV, and PWI, respectively) showing that both techniques can detect soft vulnerable plaques. The PWV estimate was more sensitive to plaque thickness compared to the SWE GV estimate. The results indicate the ability of SWE and PWI to characterize homogeneous plaques from the arterial wall.

Widman, Erik

Abstract [en]

Cardiovascular diseases are the leading causes of death worldwide and improved diagnostic methods are needed for early intervention and to select the most suitable treatment for patients. Currently, carotid artery plaque vulnerability is typically determined by visually assessing ultrasound B-mode images, which is influenced by user-subjectivity. Since plaque vulnerability is correlated to the mechanical properties of the plaque, quantitative techniques are needed to estimate plaque stiffness as a surrogate for plaque vulnerability, which would reduce subjectivity during plaque assessment. The work in this thesis focused on three noninvasive ultrasound-based techniques to quantitatively assess plaque vulnerability and measure arterial stiffness. In Study I, a speckle tracking algorithm was validated in vitro to assess strain in common carotid artery (CCA) phantom plaques and thereafter applied in vivo to carotid atherosclerotic plaques where the strain results were compared to visual assessments by experienced physicians. In Study II, hard and soft CCA phantom plaques were characterized with shear wave elastography (SWE) by using phase and group velocity analysis while being hydrostatically pressurized followed by validating the results with mechanical tensile testing. In Study III, feasibility of assessing the stiffness of simulated plaques and the arterial wall with SWE was demonstrated in an ex vivo setup in small porcine aortas used as a human CCA model. In Study IV, SWE and pulse wave imaging (PWI) were compared when characterizing homogeneous CCA soft phantom plaques. The techniques developed in this thesis have demonstrated potential to characterize carotid artery plaques. The results show that the techniques have the ability to noninvasively evaluate the mechanical properties of carotid artery plaques, provide additional data when visually assessing B-mode images, and potentially provide improved diagnoses for patients suffering from cerebrovascular diseases.